Allow shared foreign key for many2many jointable

schema/relationship.go

@@ -191,7 +191,8 @@ func (schema *Schema) buildMany2ManyRelation(relation *Relationship, field *Fiel
 		err             error
 		joinTableFields []reflect.StructField
 		fieldsMap       = map[string]*Field{}
-		ownFieldsMap    = map[string]bool{} // fix self join many2many
+		ownFieldsMap    = map[string]*Field{} // fix self join many2many
+		referFieldsMap  = map[string]*Field{}
 		joinForeignKeys = toColumns(field.TagSettings["JOINFOREIGNKEY"])
 		joinReferences  = toColumns(field.TagSettings["JOINREFERENCES"])
 	)
@@ -229,7 +230,7 @@ func (schema *Schema) buildMany2ManyRelation(relation *Relationship, field *Fiel
 			joinFieldName = strings.Title(joinForeignKeys[idx])
 		}
 
-		ownFieldsMap[joinFieldName] = true
+		ownFieldsMap[joinFieldName] = ownField
 		fieldsMap[joinFieldName] = ownField
 		joinTableFields = append(joinTableFields, reflect.StructField{
 			Name:    joinFieldName,
@@ -242,9 +243,6 @@ func (schema *Schema) buildMany2ManyRelation(relation *Relationship, field *Fiel
 
 	for idx, relField := range refForeignFields {
 		joinFieldName := strings.Title(relation.FieldSchema.Name) + relField.Name
-		if len(joinReferences) > idx {
-			joinFieldName = strings.Title(joinReferences[idx])
-		}
 
 		if _, ok := ownFieldsMap[joinFieldName]; ok {
 			if field.Name != relation.FieldSchema.Name {
@@ -254,14 +252,22 @@ func (schema *Schema) buildMany2ManyRelation(relation *Relationship, field *Fiel
 			}
 		}
 
-		fieldsMap[joinFieldName] = relField
-		joinTableFields = append(joinTableFields, reflect.StructField{
-			Name:    joinFieldName,
-			PkgPath: relField.StructField.PkgPath,
-			Type:    relField.StructField.Type,
-			Tag: removeSettingFromTag(appendSettingFromTag(relField.StructField.Tag, "primaryKey"),
-				"column", "autoincrement", "index", "unique", "uniqueindex"),
-		})
+		if len(joinReferences) > idx {
+			joinFieldName = strings.Title(joinReferences[idx])
+		}
+
+		referFieldsMap[joinFieldName] = relField
+
+		if _, ok := fieldsMap[joinFieldName]; !ok {
+			fieldsMap[joinFieldName] = relField
+			joinTableFields = append(joinTableFields, reflect.StructField{
+				Name:    joinFieldName,
+				PkgPath: relField.StructField.PkgPath,
+				Type:    relField.StructField.Type,
+				Tag: removeSettingFromTag(appendSettingFromTag(relField.StructField.Tag, "primaryKey"),
+					"column", "autoincrement", "index", "unique", "uniqueindex"),
+			})
+		}
 	}
 
 	joinTableFields = append(joinTableFields, reflect.StructField{
@@ -317,31 +323,37 @@ func (schema *Schema) buildMany2ManyRelation(relation *Relationship, field *Fiel
 				f.Size = fieldsMap[f.Name].Size
 			}
 			relation.JoinTable.PrimaryFields = append(relation.JoinTable.PrimaryFields, f)
-			ownPrimaryField := schema == fieldsMap[f.Name].Schema && ownFieldsMap[f.Name]
 
-			if ownPrimaryField {
+			if of, ok := ownFieldsMap[f.Name]; ok {
 				joinRel := relation.JoinTable.Relationships.Relations[relName]
 				joinRel.Field = relation.Field
 				joinRel.References = append(joinRel.References, &Reference{
-					PrimaryKey: fieldsMap[f.Name],
+					PrimaryKey: of,
 					ForeignKey: f,
 				})
-			} else {
+
+				relation.References = append(relation.References, &Reference{
+					PrimaryKey:    of,
+					ForeignKey:    f,
+					OwnPrimaryKey: true,
+				})
+			}
+
+			if rf, ok := referFieldsMap[f.Name]; ok {
 				joinRefRel := relation.JoinTable.Relationships.Relations[relRefName]
 				if joinRefRel.Field == nil {
 					joinRefRel.Field = relation.Field
 				}
 				joinRefRel.References = append(joinRefRel.References, &Reference{
-					PrimaryKey: fieldsMap[f.Name],
+					PrimaryKey: rf,
+					ForeignKey: f,
+				})
+
+				relation.References = append(relation.References, &Reference{
+					PrimaryKey: rf,
 					ForeignKey: f,
 				})
 			}
-
-			relation.References = append(relation.References, &Reference{
-				PrimaryKey:    fieldsMap[f.Name],
-				ForeignKey:    f,
-				OwnPrimaryKey: ownPrimaryField,
-			})
 		}
 	}
 }

schema/relationship_test.go

@@ -10,7 +10,7 @@ import (
 
 func checkStructRelation(t *testing.T, data interface{}, relations ...Relation) {
 	if s, err := schema.Parse(data, &sync.Map{}, schema.NamingStrategy{}); err != nil {
-		t.Errorf("Failed to parse schema")
+		t.Errorf("Failed to parse schema, got error %v", err)
 	} else {
 		for _, rel := range relations {
 			checkSchemaRelation(t, s, rel)
@@ -305,6 +305,33 @@ func TestMany2ManyOverrideForeignKey(t *testing.T) {
 	})
 }
 
+func TestMany2ManySharedForeignKey(t *testing.T) {
+	type Profile struct {
+		gorm.Model
+		Name         string
+		Kind         string
+		ProfileRefer uint
+	}
+
+	type User struct {
+		gorm.Model
+		Profiles []Profile `gorm:"many2many:user_profiles;foreignKey:Refer,Kind;joinForeignKey:UserRefer,Kind;References:ProfileRefer,Kind;joinReferences:ProfileR,Kind"`
+		Kind     string
+		Refer    uint
+	}
+
+	checkStructRelation(t, &User{}, Relation{
+		Name: "Profiles", Type: schema.Many2Many, Schema: "User", FieldSchema: "Profile",
+		JoinTable: JoinTable{Name: "user_profiles", Table: "user_profiles"},
+		References: []Reference{
+			{"Refer", "User", "UserRefer", "user_profiles", "", true},
+			{"Kind", "User", "Kind", "user_profiles", "", true},
+			{"ProfileRefer", "Profile", "ProfileR", "user_profiles", "", false},
+			{"Kind", "Profile", "Kind", "user_profiles", "", false},
+		},
+	})
+}
+
 func TestMany2ManyOverrideJoinForeignKey(t *testing.T) {
 	type Profile struct {
 		gorm.Model

tests/go.mod

@@ -3,17 +3,18 @@ module gorm.io/gorm/tests
 go 1.16
 
 require (
+	github.com/denisenkom/go-mssqldb v0.12.2 // indirect
 	github.com/golang-sql/civil v0.0.0-20220223132316-b832511892a9 // indirect
 	github.com/google/uuid v1.3.0
 	github.com/jinzhu/now v1.1.5
-	github.com/lib/pq v1.10.6
-	github.com/mattn/go-sqlite3 v1.14.14 // indirect
-	golang.org/x/crypto v0.0.0-20220622213112-05595931fe9d // indirect
-	gorm.io/driver/mysql v1.3.5
-	gorm.io/driver/postgres v1.3.8
+	github.com/lib/pq v1.10.7
+	github.com/mattn/go-sqlite3 v1.14.15 // indirect
+	golang.org/x/crypto v0.0.0-20220919173607-35f4265a4bc0 // indirect
+	gorm.io/driver/mysql v1.3.6
+	gorm.io/driver/postgres v1.3.10
 	gorm.io/driver/sqlite v1.3.6
 	gorm.io/driver/sqlserver v1.3.2
-	gorm.io/gorm v1.23.8
+	gorm.io/gorm v1.23.9
 )
 
 replace gorm.io/gorm => ../